The present invention relates to the imprinting of electrosensitive substrates, and more particularly to improved electrosensitive printing apparatus.
Electrosensitive papers are widely used as a printing substrate, with the advantages of high printing speeds at reasonable costs. Such substrates are typically composed of an electroconductive paper with a thin metallic overcoat. Printing occurs when a stylus bearing a desired image is brought into contact with the metallic surface layer, and a potential difference is applied between the stylus and a grounded member contacting a nearby portion of the conducting substrate. The resulting current flow is largely converted into heat at the vicinity of the stylus, resulting in the melting of the metallic layer and patterned exposure of the differently colored underlayer.
Printers used in this process have typically included a row of point stylii, with a web of electrosensitive material moving in a direction transverse to the row. By controlling the row and column printing location, such a printer creates alphanumeric characters using a dot matrix printing technique. Characters and symbols thus printed are limited in shape and resolution by the configuration of the matrix. Such technique also imposes limitations on printing speeds.
A particular problem in electrosensitive printing occurs in the imprinting of label stock and similar, die cut substrates. If the printing member and the ground electrode contact the substrate surface on opposite sides of a die cut segment, the current path between the two will be interrupted, and printing will not occur.
Accordingly, it is one object of the invention to provide fast, effective electrosensitive printing of alphanumeric characters and other symbols. A related object is flexibility in the size, shape and density of the electroprinted image. It is a further related object to avoid the limitations of point matrix printing.
Another object of the invention is the extension of electrosensitive printing to labels and other die cut substrates. A related object is the achievement of electrosensitive printing apparatus which will continuously provide a current path between the print and ground electrodes.